How Much Filling For A 12 X 18 Sheet Cake?

I'm baking a 12 x 18 sheet cake. Using butter cream icing for the outside and decorations but I have a different filling for the inside. Can someone tell me how many cups of filling is needed for this sized cake?

What kind of filling are you wanting to use?Hmmm, let's see... that's about a quarter sheet cake... I'd say two cups max on anything. If you were using something like a raspberry filling, you'd want even less to spread thinner.

Thank you for the suggestions! The filling is a cream cheese mousse. The recipe I have makes 2 1/2 to 3 cups so I'll double it and freeze the leftovers. Or make some cupcake and fill the center with the leftovers.